Fluid control valves, and valves formed of flexible materials where the material of a fluid conductor through the valve is deformed to limit or stop flow are numerous in the art. Such valves are often termed pinch valves.
FIG. 1A is a view of a round, flexible fluid conductor 11, end-on, with a frame member 13 outside the conductor and a movable pinch member 15 opposite frame member 13, in a typical arrangement for a pinch valve of the prior art. FIG. 1B shows the valve of FIG. 1A in a side view. FIGS. 1A and 1B show conductor 11 in the open position. FIG. 1C shows the pinch valve of FIG. 1A with pinch member 15 moved to pinch the valve closed, in end view as in FIG. 1A. FIG. 1D shows the valve in side view, as in FIG. 1B, but in the closed position. The view of FIG. 1C is along the section line 1C--1C of FIG. 1D. Flexible pinch valves have an advantage particularly in operations requiring feeding and flow control of chemicals and corrosive fluids, because only one material, i.e. the flexible material of the fluid conductor need be exposed to the fluid. This reduces the probability of contamination. Another advantage is that there are few moving parts, and the moving parts are outside the fluid path. Yet another advantage is that there are no seals inside the flow passage to wear and require replacement. There are some problems with pinch valves of the sort shown in FIGS. 1A, B, C, and D. One such problem is that the inside surfaces of the conductor that are pressed together to pinch off the fluid flow tend to stick together. The restoring force to open the valve after the movable pinch member is withdrawn is provided in part by the spring nature of the flexible material, and in part by any pressure applied through the fluid within the fluid conductor. In the absence of any pressure, or of quite low pressure, the restoring force is the spring nature of the material only.
Another problem often encountered is in the geometry of the passage through the flexible fluid conductor. To stop the flow entirely it is necessary that the passage be pinched closed entirely. Consider two points 17 and -9 of the normally round flow conductor 11 in the pinched condition as shown in FIG. 1C. The flexible material is severely folded at these points, and under considerable internal stress. As the valve is operated repeatedly, the material of conductor 11 at points 17 and 19 suffers fatigue and wear, and is subject to early failure, causing the valve to fail.
Yet another problem of pinch valves of the type shown by FIG. 1A through FIG. 1B is in the way that the flexible fluid conducting member is supported at points away from the pinch area. If for example, one end or the other of a flexible fluid conductor is not adequately supported, and is allowed to move under the influence of some other apparatus external to the valve, the effect may be much the same as if the pinch member moving by some amount, when in fact the pinch member has not moved at all. Flow through the valve might be slowed or stopped altogether at a time when the valve is meant to be open.
What is clearly needed is a pinch valve with a pinch member that may apply force to open the valve as well as to pinch the valve closed. More advantage will be gained if such a pinch valve has a fluid conductor passage shaped to alleviate or eliminate severe pinch points that would otherwise present regions of high stress and fatigue. Even more advantage will be gained if the valve has adequate restraints for the fluid conductor so tension or torsion in the conductor away from the pinch area will not be transferred to the pinch area.